Simulation for KAGRA cryogenic payload: vibration via heat links and thermal noise Univ. Tokyo, D1 Takanori Sekiguchi

ELiTES First Collaboration Meeting (Oct. 4th, 2012) Introduction 2 Ligo Livingston Designing of the cryogenic suspension system for KAGRA is currently in progress. Several problems/difficulties have been found for cryogenic suspensions: – Long initial cooling time (~ months) – Cryogenic compatible sensors/actuators – Extra vibrations via heat links – Suspension thermal noise

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Cryogenic Suspension Base-Line Design 3 Ligo Livingston Triple pendulum Cryogenic Spring (GAS) Pure aluminum heat links for heat extraction Test mass suspended by four thick and short sapphire fibers (Φ1.6mm, L = 30 cm)

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Today’s Topic 4 Ligo Livingston Vibration transmitted through the heat links Thermal noise of the cryogenic suspension

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Vibration via Heat Links 5 Ligo Livingston

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Vibration via Heat Links 6 Ligo Livingston Heat is subtracted from the recoil mass of intermediate stage (furthest from TM) Eight Al wires of Φ1mm x 1 m, with round shape Vertical vibration is filtered by small springs (~5 Hz) and a GAS spring (~0.5 Hz)

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Vibration via Heat Links 7 Ligo Livingston The vibration via heat links seems much below the target sensitivity level. But...

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Larger Vibration of Cryostat ?? 8 Ligo Livingston Cryostat in CLIO is vibrating at larger level than ground vibration [K. Yamamoto, 2006]. K. Yamamoto et al, J. Phys.: Conf. Ser (2006) Assuming larger vibration level of the cryostat, there are only little safety margin.

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) For Further Isolation (Suggestion) 9 Ligo Livingston Additional filter between IRM and cryostat K. Yamamoto et al, J. Phys.: Conf. Ser (2006) Vertical springs for test mass suspensions.

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Other Concerns 10 Ligo Livingston Shortcut of the vibration via actuators of intermediate mass  No problem at least for pendulum mode ?? (to be investigated more)

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Summary: Vibration via Heat Links 11 Ligo Livingston In the current design, vibration via heat links can pollute the detector sensitivity at ~10 Hz. Additional filter would be necessary for further isolation. Vibration of the KAGRA cryostat is to be measured.

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Suspension Thermal Noise 12 Ligo Livingston

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Suspension Thermal Noise Calculation 13 Ligo Livingston Rigid-body models used for seismic noise estimation. In the model, it is possible to introduce loss of the springs/ wires by adding imaginary parts to their spring constants. Suspension thermal noise can be calculated by taking imaginary part of the force-displacement transfer function.

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Suspension Thermal Noise Calculation 14 Ligo Livingston Assumed Q of suspension materials: – Sapphire fibers: 5 x 10 6 – Other suspension: 1 x 10 4 – GAS Filter: 1 x 10 3 Pendulum Q gets higher than the intrinsic material Q (dissipation dilution) Thermal noise of sapphire fiber violin modes is calculated separately and added to the rigid-body model calculation.

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Suspension Thermal Noise in KAGRA 15 Vertical bounce modes of TM & RM suspension fibers exist at Hz. Thermal noise from upper stages/recoil mass is dominant at < 20 Hz.

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) To Improve Thermal Noise 16 Ligo Livingston Test mass and recoil mass should be suspended by springs. – Eliminate annoying peaks from observation band – Improve the vertical thermal noise around 100 Hz Silicon springs might be used for large thermal conductivity and high Q.

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) To Improve Thermal Noise 17 Ligo Livingston Fibers with flexures might be useful to push the violin modes to higher frequency.

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Summary: Suspension Thermal Noise 18 Ligo Livingston Thermal noise from recoil mass suspension is dominant at Hz, and should be improved. Vertical bounce modes of the suspension fibers produce annoying peaks. Springs should be introduced.

Takanori Sekiguchi ELiTES First Collaboration Meeting (Oct. 4th, 2012) Thank you for your attention. 19 Ligo Livingston Any questions?